Vehicles comprising an internal combustion engine are subjected to a plurality of different legislative requirements and regulations. Some of these requirements and regulations are directed to fuel consumption and exhaust emission. Different countries or markets may have different requirements, but most include a specific test cycle that is supposed to give an indication of the fuel consumption and exhaust emission of the vehicle. However, there is normally a discrepancy between the fuel consumption and exhaust emission measured in a test cycle and the same measured in real world driving conditions.
Fuel consumption is one measure that is important when comparing different vehicles and it will further affect the exhaust emissions of the vehicle. A low fuel consumption is thus of advantage. Since modern vehicles are relatively optimized regarding fuel consumption, it is getting more and more difficult to reduce the fuel consumption further. At the same time, the driveability and safety of the vehicle may not be compromised.
One possibility to reduce fuel consumption is to optimize the components used in a vehicle. One such component is the fuel pump which is designed for a relatively high flow rate at a high engine speed, but which mostly is used at a relatively low flow rate, where the efficiency of the fuel pump is low.
DE 10 2004 061 249 suggests the use of two equal fuel pumps and a control unit. At low flow rates, the second fuel pump is disconnected and the control unit will control the rotational speed of the first fuel pump in dependency of the required flow rate. At higher flow rates, the first fuel pump will be connected directly to the battery such that it runs at full rotational speed, and the rotational speed of the second fuel pump will be controlled by the control unit in dependency of the required additional flow rate. The purpose of the described system is to simplify the control unit in order to reduce cost. The control unit must only be adapted to actively control half of the maximum flow rate, which reduces the size of the power semiconductors.
Even if this solution reduces the cost of the electronic control unit, it does not reduce the fuel consumption of the vehicle.
There is thus room for a fuel system that improves the fuel consumption of a vehicle.